fix: disable asyncpg prepared statement cache to prevent ProgrammingError at startup

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
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backend/app/core/database.py

@@ -9,12 +9,17 @@ from sqlalchemy.orm import declarative_base
 from app.core.config import settings
 
 # Create async engine
+# prepared_statement_cache_size=0 disables SQLAlchemy's asyncpg prepared-statement
+# LRU cache. This prevents ProgrammingError("cached statement plan is invalid") when
+# CREATE TYPE / CREATE TABLE DDL (run via create_all at startup) invalidates previously
+# cached statement plans on the same connection.
 engine = create_async_engine(
     settings.DATABASE_URL,
     echo=settings.DEBUG,
     pool_size=settings.DATABASE_POOL_SIZE,
     max_overflow=settings.DATABASE_MAX_OVERFLOW,
     pool_pre_ping=True,
+    connect_args={"prepared_statement_cache_size": 0},
 )
 
 # Create async session factory